Organic peroxides, such as peroxydicarbonates, are useful as free-radical initiators in the polymerization or copolymerization of ethylenically unsaturated monomers.
For example, organic peroxides are used as initiators in the polymerization of vinyl halides, such as vinyl chloride or vinyl bromide; vinylidene halides such as vinylidene chloride; and other compounds containing polymerizable unsaturated units. The products of this well known polymerization process have extensive commercial applications.
The polymerization of vinyl halides or the copolymerization of vinyl halides with vinylidene halides is usually conducted in an aqueous medium, i.e., emulsion, solution or suspension polymerization. In such polymerizations, the monomer or mixture of monomers is dispersed in water in the presence of a surfactant and thereafter the polymerization initiated with an organic peroxide. This is a well known reaction that has been widely reported.
All organic peroxides are by their nature hazardous materials. Their usefulness depends on their ability to decompose into free radicals, shown by the following reaction: EQU RO--OR'.fwdarw.RO.+R'O.
The rate of this decomposition reaction at any given temperature depends on the structure of R and R'.
The decomposition reaction is exothermic. If exothermic decomposition were to occur during production, storage, or shipment, when the peroxides are in a concentrated form, excess pressure development and/or fire or explosion could result. Consequently, many organic peroxides must be kept refrigerated.
There have been several reports in recent years of the retardation of the rate of decomposition of organic peroxides.
The Journal of the American Chemical Society, Volume 72, pages 1254 to 1263 (1950) discloses the use of, for example, ethyl acetoacetate, iodine, trinitrobenzene, acetanilide, nitromethane, phenol, hydrogen peroxide, and tetralin to retard the rate of decomposition of diisopropyl peroxydicarbonate.
U.S. Pat. No. 4,515,929 (1985) reports aqueous dispersions of organic peroxides including peroxydicarbonates, which are stabilized against decomposition by the addition of diphenyl peroxydicarbonate or di(alkyl substituted) phenyl peroxydicarbonates.
U.S. Pat. No. 4,552,682 (1985) discloses the use of phenolic antioxidants to retard the rate of degradation of aqueous organic peroxide dispersions. The use of phenolic antioxidants is undesirable because they result in discoloration.
U.S. Pat. No. 5,155,192 (1992) discloses the use of organic hydroperoxides, e.g., tert-butyl hydroperoxide, to retard the rate of decomposition of peroxydicarbonates.
U.S. Pat. Nos. 5,548,046 (1996) and 5,541,151 (1996) disclose the thermal stabilization of dialkyl peroxydicarbonates using unsaturated nitrites or unsaturated acetylenic compounds.